you can do it in two ways,
1st method,
64×70=4480
4480÷44.8
64-44.8=19.2
2nd method,
you have to find the common multiplier,
to find the common multiplier you have to decrease the percentage by 100 and divide it by 100,
100-70=30
30÷100=0.3
now you have to multiply 0.3 and 64,
0.3×64=19.2
either way, you'll get the answer, 19.2
hope this helps....